Serotonin – The Happiness Molecule

What is serotonin? 

Serotonin is a neurotransmitter, a signalling molecule that allows communication within the central nervous system and throughout the body via the peripheral nervous system. It is probably most widely known as a mood regulator – our in-built ‘happy’ molecule. But serotonin also plays a role in learning, memory formation, regulating body temperature, sensitivity to heat and pain, sleep quality and appetite regulation.  It is no wonder that an imbalance in serotonin levels can have such widespread impacts on many body systems. 

How would I know if my child has low serotonin? 

Low serotonin levels are associated with mood disorders, including depression and anxiety, digestive dysfunction, and sleep dysregulation

Signs that someone may be low in serotonin include:

  • Anxiety – which may be worse in the winter months
  • Winter blues or seasonal affective disorder
  • Panic attacks and phobias
  • Obsessive thoughts or behaviours
  • Perfectionism or being overly controlling 
  • Irritability
  • Depression or low mood
  • Suicidal thoughts
  • Low self-esteem 
  • PMS
  • Sensitivity to hot weather
  • Hyperactivity
  • Anger or rage
  • Digestive issues
  • Insomnia or sleep disturbance
  • Afternoon or evening cravings for carbohydrates

If you or your child exhibits six or more of these symptoms, consider that low serotonin may be a contributing factor. 

Winter blues

Does your child’s mental health take a nosedive in the winter months? Perhaps you notice an increase in anxiety or OCD behaviours; they may have trouble sleeping or become more irritable or angry than usual as the nights get longer. 

These symptoms could be due to a sharp dip in the body’s serotonin levels as exposure to natural sunlight decreases. A 2002 study published in The Lancet found that the serotonin production rate in the brain decreased proportionally in response to a drop in exposure to bright sunlight and increased again with exposure to full-spectrum light. The exact mechanism by which this happens is not fully understood. Still, sunlight is thought to play a role in activating the synthesis of serotonin and may also influence the activity or number of receptor sites for serotonin in the brain.


Serotonin and sleep

Serotonin is a precursor of melatonin – the hormone that regulates circadian rhythm and helps maintain a healthy sleep cycle. This can explain why insomnia and sleep disturbances can follow when serotonin is in short supply. To further complicate the picture, in some patients with autism spectrum disorder (ASD), research suggests that there may be a disruption in the biochemical pathway that converts serotonin to melatonin, leading to depleted melatonin levels, despite normal or high levels of serotonin in the blood.


Other factors that influence serotonin and melatonin levels 

While sunlight exposure may play a crucial role in maintaining serotonin levels, nutritional factors also come into play:

  • Adequate vitamin D is needed to make serotonin. Most people in the UK have insufficient vitamin D levels, which is also dependent on sunlight exposure. It is worth checking vitamin D levels regularly and supplementing as necessary, especially between October and May in the UK. 
  • B vitamins (especially B6), zinc and magnesium, are all needed as co-factors in the production of serotonin. If these are in short supply in the diet, or if there is a functional deficiency of any of these nutrients, for example, in the condition kryptopyrroluria, serotonin production will not be optimal. 
  • The building block of serotonin is the amino acid tryptophan. Tryptophan is an essential amino acid, meaning that our bodies cannot make it, so we must ingest it through the diet. Tryptophan is converted to 5-hydroxytryptophan (5HTP), which is converted to serotonin. If tryptophan is in short supply, either through inadequate protein intake, poor breakdown or protein absorption, serotonin levels may drop. 


How to optimise serotonin production

So how can we help support optimal levels of serotonin all year round? 

  • Ensure adequate intake of tryptophan in the diet. Tryptophan-rich foods include white meat, especially turkey, salmon, oats, whole milk, pumpkin seeds and banana. 
  • Monitor vitamin D levels and supplement as necessary.* You can buy home test kits to measure vitamin D. The UK recommended daily vitamin D intake is 10 μg/day for all age groups.
  • Ensure adequate intake of B vitamins, zinc and magnesium. These are all required for the conversion of tryptophan to serotonin. 
  • If you are experiencing symptoms of low serotonin, especially during the winter months, consider taking supplementary tryptophan and/or 5HTP.*
  • Consider light therapy. Research has found that light therapy is an effective treatment for seasonal affective disorder, raising serotonin levels in the blood and increasing the brain’s receptivity to serotonin. We recommend the Human Charger. This headset is lightweight and comfortable to wear. It exposes receptors in the brain directly to light via the ear canals. It is ideal for children and teenagers since it does not require them to sit still, only needs to be worn for a few minutes per day, and allows the user to listen to music at the same time as receiving the light therapy. 


Working with your practitioner

A qualified nutritional therapist or functional medicine practitioner can help you establish whether serotonin insufficiency may contribute to your child’s symptoms. We can use a range of functional and medical tests to investigate this, including urine organic acid testing and blood tests. We can also look at nutritional status, genetics and lifestyle to ascertain how these may impact the metabolism and regulation of serotonin and other neurotransmitters. 

Book your free Discovery Call today to talk to one of our practitioners about working with us. 

*before introducing any nutritional supplements, please seek the advice of a qualified nutritional therapist or functional medicine practitioner. 



  2. Trudi Scott – the anti-anxiety food solution
  3. Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sunlight and season on serotonin turnover in the brain. Lancet. 2002 Dec 7;360(9348):1840-2. doi: 10.1016/s0140-6736(02)11737-5. PMID: 12480364.
  4. Sansone RA, Sansone LA. Sunshine, serotonin, and skin: a partial explanation for seasonal patterns in psychopathology? Innov Clin Neurosci. 2013 Jul;10(7-8):20-4. PMID: 24062970; PMCID: PMC3779905.
  5. Spindelegger C, Stein P, Wadsak W, et al. Light-dependent alteration of serotonin-1A receptor binding in the cortical and subcortical limbic regions in the human brain. World J Biol Psychiatry. 2012;13:413–422.
  6. Pagan, C., Delorme, R., Callebert, J. et al. The serotonin-N-acetylserotonin–melatonin pathway as a biomarker for autism spectrum disorders. Transl Psychiatry 4, e479 (2014).
  8. Terman, M. and Terman, J.S., 2005. Light therapy. Principles and practice of sleep medicine, 4, pp.1424-1442.
  9. Tyrer, A.E., Levitan, R.D., Houle, S., Wilson, A.A., Nobrega, J.N., Rusjan, P.M. and Meyer, J.H., 2016. Serotonin transporter binding is reduced in seasonal affective disorder following light therapy. Acta Psychiatrica Scandinavica, 134(5), pp.410-419.
  10. Rao, M.L., Müller‐Oerlinghausen, B., Mackert, A., Strebel, B., Stieglitz, R.D. and Volz, H.P., 1992. Blood serotonin, serum melatonin and light therapy in healthy subjects and in patients with nonseasonal depression. Acta Psychiatrica Scandinavica, 86(2), pp.127-132.